sdl2 - Render to texture and then to screen cause flickering

So I have my class vItem which has a vector (consider elements like layers) of textures, origin rects and destination rects plus other stuff.
Basically whenever I update any of the layers in the vector I redraw everything on an internal texture which is then displayed on the screen, here's the function that draws on the texture:

void vItem::draw(){
    if(sprites.size() <= 0)
        return;


    // This calculates the dimensions of a rectangle big enough to contain every texture
    SDL_Point size = calculateSpriteRect();

    if(size.x <= 0 || size.y <= 0)
        return;

    // If the final texture does not exists or its dimensions are different from the new rectangle I destroy it and recreate it
    if(final_sprite == NULL || size.x != final_sprite_size.x || size.y != final_sprite_size.y){
        if(final_sprite != NULL)

            SDL_DestroyTexture(final_sprite);
        final_sprite = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, size.x, size.y);
        SDL_SetTextureBlendMode(final_sprite, SDL_BLENDMODE_BLEND);
        final_sprite_size = {size.x, size.y};
    }

    SDL_RenderPresent(renderer);
    SDL_SetRenderTarget(renderer, final_sprite);
    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
    SDL_RenderClear(renderer);

    for(int i = 0; i < sprites.size(); i++){
        SDL_SetTextureAlphaMod(sprites[i].sprite, sprites[i].alpha);
        SDL_RenderCopy(renderer, sprites[i].sprite, &sprites[i].source, &sprites[i].bounds);
    }   
    SDL_RenderPresent(renderer);
    SDL_SetRenderTarget(renderer, NULL);
}

The problem comes after this function: I have a child class of vItem called vButton where I have two layers of text (one normal and the other on for when the mouse is over the button), and when I update alpha values of the layers to hide one level and show the other one draw() is called. This transition causes an instant flickering (black background right before drawing).
When I removed vSync I noticed that this wasn't happening anymore, but I need vSync.

UPDATE:
Ok... Apparently if I remove both SDL_RenderPresent(renderer); the flickering is gone and everything is rendering correctly, but I can't understand why. This is the final function:

void vItem::draw(){
    if(sprites.size() <= 0)
        return;

    // This calculates the dimensions of a rectangle big enough to contain every texture
    SDL_Point size = calculateSpriteRect();

    if(size.x <= 0 || size.y <= 0)

        return;

    // If the final texture does not exists or its dimensions are different from the new rectangle I destroy it and recreate it
    if(final_sprite == NULL || size.x != final_sprite_size.x || size.y != final_sprite_size.y){
        if(final_sprite != NULL)
            SDL_DestroyTexture(final_sprite);
        final_sprite = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, size.x, size.y);
        SDL_SetTextureBlendMode(final_sprite, SDL_BLENDMODE_BLEND);
        final_sprite_size = {size.x, size.y};
    }


    //SDL_RenderPresent(renderer);
    SDL_SetRenderTarget(renderer, final_sprite);
    //SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
    //SDL_RenderClear(renderer);
    for(int i = 0; i < sprites.size(); i++){
        SDL_SetTextureAlphaMod(sprites[i].sprite, sprites[i].alpha);
        SDL_RenderCopy(renderer, sprites[i].sprite, &sprites[i].source, &sprites[i].bounds);
    }   
    //SDL_RenderPresent(renderer);

    SDL_SetRenderTarget(renderer, NULL);
}

How can the renderer keep information about the texture on texture rendering and texture on screen rendering at the same time (since I have only one SDL_RenderPresent() left at the end of my game loop)? Is it meant to work like that?